The present invention is related to Japanese patent application No. 2000-198550, filed Jun. 30, 2000; the contents of which are incorporated herein by reference.
The present invention relates to a fuel supply system having a fuel pump in a sub-tank, and more particularly to a fuel supply system provided with a jet pump for supplying a fuel from the exterior of a sub-tank to the interior thereof.
Fuel supply systems are provided with a sub-tank in a fuel tank. Fuel pumps in the sub-tank have heretofore been known. Such fuel supply systems include a fuel supply system provided with a jet pump for supplying fuel from the exterior of the sub-tank to the interior thereof. The jet pump has a nozzle adapted to eject fuel into a throat provided in a bottom portion of the sub-tank. The fuel ejected from this nozzle is supplied from the throat to the interior of the sub-tank, and the fuel in the exterior of the sub-tank is sucked into the throat by utilizing a negative pressure occurring in the throat, the fuel sucked into the throat being supplied to the interior of the sub-tank.
The sub-tank is provided therein with a check valve for preventing the fuel in the sub-tank from flowing to the exterior thereof through the throat. In recent years, there has been a demand that the quantity of fuel initially supplied on a vehicle assembly line or temporarily supplied when gasoline is low, be reduced. In order to reduce the quantity of fuel initially supplied, it is necessary that a check valve be opened during a low fuel level. In this case, the check valve may be put in a substantially vertically extending condition during valve closing so that a valve opening pressure due to the weight of the check valve itself becomes low. However, a seal seat surface of the check valve must be secured on a circumferential edge portion of an outlet of a throat. Therefore, in order to put the check valve in a substantially vertically extending condition during valve closing, it is necessary that the outlet of the throat be raised at least by a height corresponding to the height of the seal seat surface from a bottom surface of a tank.
In the case of such fuel supply system of a related art design in which the throat is disposed horizontally with respect to the bottom surface of the tank, an inlet of the throat must also be raised. This causes an ineffective residual quantity of fuel in the fuel tank which cannot be sucked up by a jet pump.
When the throat is lowered to the bottom surface of the tank to reduce the ineffective residual quantity of fuel, a seal seat surface of the check valve 110 can be secured on the circumferential edge portion of the outlet of the throat 100 by inclining the same outlet as shown in FIG. 6. However, since a valve opening pressure due to the weight of the check valve 110 itself increases in this case, fuel level increases in the fuel tank at which the check valve 110 can be opened.
The present invention has been made in view of the above-mentioned drawbacks, and provides fuel supply system capable of reducing the quantity of fuel initially supplied and any ineffective residual quantity of fuel.
According to an aspect of the present invention, the fuel supply system has a throat provided in a bottom portion of a sub-tank so that the throat inclines with respect to a bottom surface of the sub-tank. The height of the throat increases gradually from a suction port thereof toward a supply port thereof. A plane of an opening of the supply port extends substantially vertically.
Accordingly, a seal seat surface for a check valve can be secured on a circumferential edge portion of the opening of the supply port provided in a position higher than the suction port, so that the check valve can be set substantially vertical during valve closing. This prevents a valve opening pressure due to the weight of the check valve itself from increasing. Therefore, the check valve can be opened at a low fuel level, and the quantity of fuel initially supplied into fuel tank can be reduced.
Since the throat is inclined with respect to the bottom surface of the sub-tank, the suction port thereof can be lowered to the same bottom surface. This enables the ineffective residual quantity of fuel in the fuel tank, which cannot be sucked up by a jet pump, to be reduced.
According to another aspect of the present invention, the fuel supply system has a throat provided in a bottom portion of a sub-tank so that the throat inclines with respect to a bottom surface of the sub-tank. The height of the throat increases gradually from a suction port thereof toward a supply port thereof. A plane of an opening of the supply port crosses the axial direction of the throat substantially at right angles.
According to this structure, a seal seat surface for a check valve can be secured on a circumferential edge portion of the supply port provided in a position higher than the suction port, and the check valve can be set substantially vertical during valve closing by setting an angle of inclination of the throat to such a level that permits the seal seat surface to be secured. This can prevent a valve opening pressure due to the weight of the check valve itself from increasing. Therefore, the check valve can be opened at a low fuel level, and the quantity of the fuel initially supplied to the interior of fuel tank can be reduced. Since the throat is inclined with respect to the bottom surface of the sub-tank, the suction port can be lowered to the same bottom surface. This enables the ineffective residual quantity of the fuel in the fuel tank which cannot be sucked up by a jet pump to be reduced.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In the drawings: